Photographic developing medium producing fine grain results



Patented May 2, 1939 UNITED STATES PHOTOGRAPHIC DEVELOPING MEDIUM PRODUCING FINE GRAIN RESULTS Garnet P. Ham, Old Greenwich, Conn., aasignor to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application March 16, 1938, Serial No. 196.15!

Claims. ((1855-88) This invention relates to a photographic developer and more particularly. to a developer capable of giving a fine grain. The necessity of great enlargement which is 5 increasingly important with the advance of the miniature camera and also the need for motion picture positive film has made it necessary to depart from some of the standard developers used in the development of films where great enlargement and hence extreme fine grain was not necessary. This has resulted in the development of innumerable fine grain developers in the past two years. These developers have followed along three main lines.

One class of developer using the standard Metol and hydroquinone with very low alkalinity given by borax or similar weak alkalies used in small quantities does not sacrifice the speed of emulsion to any serious extent but results in a grain which, while finer than those produced by standard developers, leaves much to be desired in the case of finer grain films.

The second class of developers is represented by those using p-phenylenediamine as their base with or without Glycine and small amounts of Metal. This class of developers gives an extremeiy fine grain but at the expense of contrast and particularly, of emulsion speed. In other words, greatly increased exposure is necessary. 30 A third class of fine grain developers is represented by the so-called'physical developers in which colloidal silver is plated out onto a latent image on the film. This type oi developer with suitable skilled operation is capable of giving a due grain but is more difficult to use than those depending on chemical action.

It has been proposed recently to combine chemical developers with physical developers. This is frequently referred to in the art as silver load- 40 ing a developer and .among the most successful compromise developers 0! this type is the wellknown Champlin having the following formula in which the parts are by weight except in the cases of the water and the isopropyl alcohol where the corresponding volumes are given:

for most uses but they are subject to certain disadvantages. The p-phenylenedlamine developers as noted above require a greatly increased exposure wlth high speed panchromatic films and as ,these films are being increasingly used because of their high speed, this disadvantage is extremely serious. Most fine grain developers, even those of the Metol-hydroquinone type, likewise require for the production of real fine grain a considerable underdeveiopment so that the resulting negatives are of relatively low contrast, a gamma 0! about 0.7 being often recommended with these developers. This is a serious disadvantage in the case of many negatives because in order to compensate for the low contrast of the developed negative it is necessary to use printing papers of excessive contrast and as is well known, the emulsion character and general tone and gradation of high contrast papers are not as desirable as those of softer papers.

According to the present invention, a developer of the combined chemical and physical type is produced which gives a grain as fine and in some cases finer than the best obtainable with the fine grain developers known at the present time without possessing their disadvantages. The developer of the present invention does not reduce the emulsion speed; in fact, as compared to the best of the compromise fine grain developers on the market at the present time, it shows a slight increase in emulsion speed amounting to from -30%. Another important advantage of the present developer is that it is not necessary in order to obtain fine grain to underdevelop the negativevproducing a fiat negative of excessively low contrast. 0n the contrary, the developing time can be increased to produce a negative of normal contrast (when compared with negatives developed in standard developers which are not fine grain) without loss of the fine grain. This is an important advantage because extreme fineness of grain has been accorded an importance entirely out of proportion to the real facts. Standard fine grain developers now available will give a sufficiently fine grain even with fast panchromatic film such as the standard Eastman Super X to permit enlargement to adequate size for 99% of the work actually undertaken. The other factors such as contrast of the negative, emulsion speed and the like are in many,ii not most, cases more important. It is an outstanding advantage of the present invention that the developer meets all of the requirements and does not compromise with speed or quality.

A developer of the present invention consists in a chemical developer which may be of various formulation but preferably a p-phenylene diamine base developer to which sumclent Metol has been added for adequate shadow detail,

standard preservative such as sodium sulfite, buffers and alkali combined with colloidal silver or silver compounds stabilised with a protective colloid. To obtain the full results, the developer should also be activated by exposure to actinic ll ht.

I have found that it is not necessary to use an extremely narrow range of proportions of chemical developers. The choice of protective colloid is also very wide. Gelatin, alkyl cellulose, water-soluble polyvinyl alcohol and many other colloids can be used provided, of course, that the colloid does not react with the chemical components of the developer. The activated silver chloride is prevented from precipitation by the colloid and apparently plates out on the latent image as the latter is formed by the action of the chemical developers. The appearance of the negative closely resembles that obtained by a true physical developer but the action and the time of development correspond to that of a chemical developer of the character represented by the chemical constituents of the developer of the present invention. I believe that the fineness of grain without sacrifice of emulsion speed is in large measure due to the fact that the physical development is kept in proportion to the chemical development by the presence of the colloid which prevents premature decomposition of the silver halide in the developer. The present invention is, however, not intended to be limited to any theory of action.

The developer of the present invention possesses an extraordinary stability both of high temperatures and to very low temperatures. Thus, for example, tests with the developer which is described in the specific examples below were made at 120 F., the temperature frequently reached in the mail rooms of steamers in the tropics. After thirty days at 120 F., the developer showed but little precipitate and its developing action was almost indistinguishable from that of fresh developer. A month's storage in a refrigerator at a temperature only a. little above freezing showed no noticeable effect. Under similar treatment, Champlin #15 showed marked decomposition at 120 1". and when used for developing films gave a lower range of detail and showed amarkedlydeoreased speed, thatistosay, an exposure of almost double was required with Super 1: in order to obtain the same results.

A further important advantage of the developer of the present invention lies in the fact that it is relatively insensitive to temperature. Development can be carried out at 70' F. or even materially higher (with, of course, a corresponding shortening of developing time) without any noticeable loss of fineness of grain or contrast in the negative.

The developer of the present invention gives excellent results with all kinds of film including slow and fast panchromatic, orthochromatic, motion picture positive and other negative material. The advantages of maintenance of emulsion speed are particularly noticeable with fast panchromatic films. As is well-known. there is comparatively little decrease in emulsion speed with the usual fine grain developer in the case of slow speed, ultrafinegrain panchromatic film and the high inherentcontrastofthistypeofmateiialmakes.

the underdevelopment required by the usual fine grain developer relatively unobiectionable, It is an advantage of the present invention that the developer-isusefulforallofthe types of negative material even though its greatest advantages over known developers are to be found Example 1 A solution is prepared having the following composition:

5 Parts Paraphenylenediamine 5.! Metol 1.5 Glycin 5.7 Sodium sulphlte 84.0 Boric acid. 1.3 Salicylic acid 0.2 Benzoic acid 1.02 Water to make 500.0

A second solution is prepared having the following composition:

Parts Potassium chloride 0.25 Egg albumen 0.1-0.5 Silver nitrate 0.25 Water 100.00

The silver chloride formed in this solution is prevented from precipitating by the colloidal albumen present. The mixture is then activated by actinic light for a period oi time varying from 5 to 15 minutes or even longer depending on the volume of the solution treated, the intensity of the light, etc. The time is not critical and longer activation does no harm. After activation is complete, the solution is added to the first solution and the mixture is permitted to ripen for from 1 to 8 hours at ordinary room temperature. preferably in the absence of strong actinic light. At the end of this period, a certain amount of silver coagulate will be noted and this is filtered oil. The remaining clear solution. which is very light amber in color, is bottled and constitutes the finished product which is used at full strength.

The final solution is thoroughly light stable and does not have to be stored in dark bottles.

It keeps for months and can be used repeatedly.

Thus, for example, a pint of developer can be used to develop from 6 to 10 standard thirty-six exposure rolls of 35 mm. film without any noticeable loss in quality oi the negative. Care, of course, is taken to increase the developing time with each roll. This represents a considerably longer life than any oi the standard fine grain developers at present available.

Development is,preferably efl'ected at ordinary room temperature of about 70 F. but satisfactory results can be obtained at 65 F. and higher temperatures can also be used. The development time will vary with difi'erent films; for example, satisfactory contrast for use with the ordinary grades of paper on last panchromatic film such as Eastman Super x is obtained by developing at 70 F. for 18 to 25 minutes in fresh developer depending on the degree of agitation. There is no tendency to deposit stains on the film and completely stagnant development can therefore be used which is an added convenience where facilities for continuous agitation are lacking. Slow panchromatic iilm of the type marketed by Eastman Kodak as Panatomic, by Du Pont as Micropan and by the Agfa Ansco Company as Finopan require shorter development time.

I have not determined just what takes place during activation of the silver halide and after addition to the chemical developing solution and the present invention is not limited to any theory of action. However, I believe that it is probable that far-reaching photo-activation oi the silver halide takes place because there is some precipitate during activation in spite of the presence of the protective colloid. When the two solutions are mixed, some of the activated silver halide reacts with the chemical developing agents as there is a considerable precipitation of silver. I believe that this action proceeds only to the point at which the most strongly activated silver halide particles are attacked. During development there is a marked plating out of silver onthe image as it forms by the action of the chemical developing agents and I believe that the activated silver halide or in some cases colloidal silver kept from precipitating by the protective colloid tends to plate out on the developing image with great rapidity. The plating action takes place much faster than with a pure physical developer.

As has been stated above, the egg albumen is merely representative of a number of protective colloids which appear to act because of their colloidal properties. Albumen gives very satisfactory results and is the preferred colloid but other colloids can be used. The proportions of the chemicals may be varied within wide limits and other chemical developing agents such as hydroquinone may be included.

Example 2 Two solutions are prepared as in Example 1 but water-soluble methyl cellulose is substituted for the egg albumen. The solutions are then mixed and subjected to activation with actinic light for from five to fifteen minutes or longer, followed by ripening at room temperature for from one to eight hours and filtering oil the silver coagulate formed. The solution is of substantially the same light color as that of the first example.

The procedure described above in which mixing the solutions precedes light activation is simpier and gives results which are indistinguishable from those produced by separately activating the silver halide solution before mixing.

The developer does not appear to be extremely sensitive to slight changes in pH. However, the presence of buffers and preservatives for the colloid are desirable.

The production of activated silver halide solution can use various alkali metal chlorides or iodides. The potassium chloride of the examples gives excellent results but satisiactory results are obrainable with the iodide or with the chloride or iodide of sodium. The bromide is less desirable as it forms a silver compound which is excessively activated resulting in a loss of a large portion of the silver by precipitation. Mixtures of the alkali halides may also be used and ii the amount of bromide present is small, such mixtures even though containing bromide give satisfactory results.

What I claim is:

1. A photographic developer comprising an aqueous dispersion containing unoxidized metal a colloidal silver halide and a protective colloid.

2. 'A photographic developer comprising an aqueous dispersion containing unoxidized metal a colloidal light-activated silver halide and a protective colloid.

3. A photographic developer comprising an aqueous dispersion containing p-phenylenediamine, Glycine and Metol, preservatives, colloidal light-activated silver halide and a protective colloid.

4. A photographic developer comprising an aqueous dispersion containing p-phenylenediamine, Glycine and Metol, preservatives, colloidal light-activated silver halide and albumen.

5. A method of producing a photographic developer which comprises forming an aqueous dispersion of an alkali metal halide, a protective colloid and silver nitrate, subjecting the dispersion to the action of actinic light, adding to the dispersion an aqueous solution of organic chemical developing agents and at least one preservative, permitting the mixture to stand until precipitation has substantially ceased and removing the precipitate by'flltration, the amount of organic chemical developing agents being largely in excess of that capable of reacting with the silver halide formed so that the dispersion contains unoxidized organic chemical developer.

6. A method of producing a photographic developer which comprises forming an aqueous dispersion of an alkali metal halide, a protective colloid and silver nitrate, subjecting the dispersion to the action of actinic light, adding to the dispersion a solution containing p-phenylenedlamine, Glycine and Metol, permitting the mixture to stand until precipitation has substantially ceased and removing the precipitate by filtration, the amount of paraphenylenediamine, Glycine and Metol being largely in excess of that capable of reacting with the silver halide formed so that the dispersion contains unoxidized paraphenylenediamine, Glycine and Metol.

'7. A method of producing a photographic developer which comprises forming an aqueous dispersion of an alkali metal halide, albumen and silver nitrate, subjecting the dispersion to the action of actinic light, adding to the dispersion a solution containing p-phenylenediamine, Glycine and Metol, permitting the mixture to stand until precipitation has substantially ceased and removing the. precipitate by filtration, the amount of paraphenylenediamine, Glycine and Metol being largely in excess of that capable of reacting with the silver halide formed so that the dispersion contains unoxidized paraphenylenediamine, Glycine and Metol.

8. A method of producing a photographic developer which comprises forming an aqueous dispersion of an alkali metal halide, a protective colloid and silver nitrate, adding this dispersion to an aqueous solution of chemical developing agents and preservatives, subjecting the mixture to the action or actinic light. permitting the activated mixture to stand until precipitation has substantially ceased and removing the precipitate by filtration, the amount 01' organic chemical developing agents being largely in excess of that capable of reacting with the silver halide formed so that the dispersion contains unoxidized organic chemical developer.

9. A method of producing a photographic developer which comprises forming an aqueous dispersion of an alkali metal halide. a protective colloid and silver nitrate, adding this dispersion to an aqueous solution containing p-phenylenediamine, Glycine and Metol and preservatives,

subjecting the mixture to the action of actinic one solution containing p-phenylenediamlne, Glycine and Metal and preservatives, subjecting the mixture to the action of aetinic light, permitting the activated mixture to stand until precipitation has substantially ceased and removing the precipitate by filtration, the amount oi paraphenylenediamine, Glycineand Metol being largely in excess oi that capable of reacting with the silver halide formed so that the dispersion contains unoxidized Glycine and Motel.

GARNET P. HAM.

CERTIFICATE or CORRECTION.

Patent no. 2,156,626.

GARNET P. am.

May 2, 19 9.

It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correction as follows:

Page 5, first column, line 75, and second column, line 1, claims 1 and 2 respectively,

for "meta1" readlleto1,; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 50th day of May, A. n. 1939.

(Seal) Henry Van Arsdale Acting Commissioner of Patents.

paraphenylenedlamine, I 0

one solution containing p-phenylenediamlne, Glycine and Metal and preservatives, subjecting the mixture to the action of aetinic light, permitting the activated mixture to stand until precipitation has substantially ceased and removing the precipitate by filtration, the amount oi paraphenylenediamine, Glycineand Metol being largely in excess oi that capable of reacting with the silver halide formed so that the dispersion contains unoxidized Glycine and Motel.

GARNET P. HAM.

CERTIFICATE or CORRECTION.

Patent no. 2,156,626.

GARNET P. am.

May 2, 19 9.

It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correction as follows:

Page 5, first column, line 75, and second column, line 1, claims 1 and 2 respectively,

for "meta1" readlleto1,; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 50th day of May, A. n. 1939.

(Seal) Henry Van Arsdale Acting Commissioner of Patents.

paraphenylenedlamine, I 0 

